Climate 302 C EXAM 2

t=

(-1/lambda ln(N/Nsubscript0))

What determines isotope fractionation?

- Temperature: colder temperature: more O18 depletion (more negative δO18) - Condensation: preferentially remove O18 (heavier isotope) - Evaporation: preferentially remove O16 (higher isotope)

A.E. Douglass

Considered the Father of Tree Ring Research. He figured out how old a tree was when it was cut by matching its ring pattern with living trees.

t(avg)=

1/lambda It is the average time each radiocarbon atom spends in a given sample until it decays is 8270 years.

Coral Chronology

1: Aragonite skeleton of massive corals often exhibit annual density banding 2: Similar to Radiometric dating with Carbon 14 To measure on a mm scale, use a dental drill (very frequent) To measure on a micrometer scale, use a e-beam or laser (less frequent)

Long-term δ18O trend in the deep ocean as measured from the calcite shells of foraminifera(Two Factors)

1: Changes in Ocean Temperature 2: Growth of ice sheets on land that are O-16 enriched

What Influence Lake Varves?

1:Summer temperature: can be used for inferences about past high latitude summer temperature changes 2: Winter Snowfall 3: Rainfall - The latter two factors can be used to estimate past drought and precipitation patterns.

Correlation Techniques

1:Tuning- consists of matching a climate proxy record to a selected target curve Matching is accomplished by changing the chronology of the record so that it correlates better with the target curve.

Tectonic Scale Climate Changes

4 PROCESSES!!!! 1. Land Ocean spatial configuration: Control where ice sheets form 2. Spread of Sea floor: volcanoes and oxidation of organic carbon in sedimentary rocks, control release of CO2 in the atmosphere 3. Chemical Weathering: Control CO2 removal process, a thermostat of the Earth's climate 4. Uplift-mountain effect: expose fragmented and fresh rock for chemical weathering

Climate Change through the Years

580-400 MY: Climate was generally coldest 255-65 MY: climate was warmest with the warmest during the mid-Cretaceous (100MY) 65-0MY: Earth's climate became colder with time

Is Coral signal biological or climatic in origin?

?????? (find answer!)

What Radioactive Decay Does

A Neutron emits an electron and becomes a proton Occurs at a predictable, constant rate

Sediment Varves

A pair of thin sedimentary layers formed annually by seasonal climatic changes. Sedimentary varved deposits can be found in lacustrine and sometimes even in marine settings. Varved sediments can be formed from biological and sedimentologic processes, both of which are often influenced by climate variations.

Radiocarbon and Organisms

All living organisms establish the same C-14/C-12 ratio as that of the atmosphere When an organism dies the C-14 isotope decays at the constant rate of 5730 according the well known decay law. As a result, the C-14/C-12 Ratio decreases, and the age of a sample can be measure by determining the Ratio.

Lacustrine Varves

Also known as lake sediments. Great in arid terrestrial regions and latitudes poleward of treeline. If these varves can be independently confirmed through radiometric dating, they can provide seasonal/interannual resolution over centuries/ millennia.

Extending the Calibration Curve

An active area of research is attempting to extend this curve farther and farther back in time. This is done NOT with tree rings, but with speleothems and varvd sediments.

Isotopes

An element with additional neutrons than it would normally have (same number of protons and electrons)

Sensitive vs. Complacent Series

An example is if you are lookng for drought stress in an area, don't go to the area that would have the most water in the area (bottom of the canyon) rather go to the place where drought would most affect a plant (steep hillside with shallow soil). Canyon = complacent Hillside = Sensitive

Ice Cores

Annual layers of snowfall in ice cores can be counted similar to tree rings. Distinct annual layers stand out because in snow that falls in SUMMER, CRYSTALS ARE LARGER AND ACIDITY HIGHER than in winter snow. Scientists now can even tell seasons apart using a laser to measure the concentration of dust particles.

Exceptions to Radiocarbon Dating Techniques

Annually Datable Archives such as tree rings, coral, and layered lake sediments

Earth during the Winter Solstice

Axis away from Sun Vertical rays on Tropic of Capricorn (23.5°S Lat) 24-hr night above Arctic Circle (66.5°N Lat) 24-hr day below Antarctic Circle (66.5°S Lat)

Earth during the Summer Solstice

Axis toward Sun Vertical rays on Tropic of Cancer (23.5°N Lat) 24-hr day above Arctic Circle (66.5°N Lat) 24-hr night below Antarctic Circle (66.5°S Lat)

Cenozoic Climate Change

BLAG hypothesis cannot explain the divergence of the curve at 15 million years

Why Does O-18 Concentration Decrease with Temperature?

Because as the temperature increases, O-16 will be evaporated first over O-18, while O-18 condenses first (O-16 is lighter). This is also called Isotope Fractionation

Organics

Biological Response to Temperature and Salinity

Speleothems

Calcium Carbonate- Cave Deposits Grows on Scale of 10's of microns/year Can get records of TENS OF THOUSANDS OF YEARS O-18 is used for paleoclimate reconstruction of monsoons O-18 of caves is a reflection of O-18 in water, and ultimately a reflection of rainfall in the region

One big reason the dinosaurs disappeared

Climate Change

Ecological Amplitude

Climate Stress is greater at species margins

Time Scales of Climate Variation

Climate Varies on all timescales ranging from sub annual to tectonic

Earth during the Fall/Spring Equinoxes

Day=Night at all points

More on Tree Rings

Dendrochronology is crossdating Tree Rings are not counted or read Crossdating should make dating errors of tree rings 0, and uses ONLY the tree rings themselves.

Notes about proxies

Direct Measurements have limited time frames Historical records are often qualitative and incomplete Geological Archives provide both indirect qualitative and quantitative data, but qualitative data varies in temporal resolution Proxies are NOT a direct measurement of climate, but rather a response to some component of the climate

Earth's Orbit over Time

Eccentricity Varies from 0 to .0605 (today it's .0167) Varies from near circle to ellipse with a period of 100,000 years Distance to Sun changes leads to insolation changes

Marine Sediments (2 types)

Foraminifera and Organics

How a Glacial Ice Sheet Forms

Force balance on an ice sheet Surface slope leads to pressure gradient Pressure gradient opposed by shear stress Ice responds be deforming = creep flow At Equilibrium at balance b/w accumulation at top and ablation at margins

Marine Sediment Varves

Found in Santa Barbera Cariaco and Orca. These are produced by seasonal variations in surface productivity. The oceanic oxygen minimum zone is ideal for preservation of annual records because the zone inhibits activity in the sediments. These preserves provide finescale laminations of seasonal sedimentation.

Model Validation Strategy

Goal: Calibrate model on a set of data, and validate the model on an independent set of data. Use the CROSS VALIDATION METHOD (also know as the leave one out method)

Uplift Weathering Hypothesis

High relief due to uplift has increased silicate weathering causing a draw down of CO2, thus cooling the climate

High Resolution Proxies (less than 100,000 years)

Instruments- 150 years Historical- 400 years Tree Rings- 500 years Ice Cores- 20,000 years Lake Sediments- 30,000 years

C-14

It is the longest lived radioactive isotope of carbon. Occurs naturally in the atmosphere at an equilibrium level of 1:10^12 relative to the most abundant Carbon 12 The Carbon 14 formed is rapidly oxidized to CO2-14 and mixes with the rest of the CO2 in the atmosphere

Example of Proxy Data

Leaves! Serrations of Leaf indicate temperature -Jagged means colder climate Leaf Waxiness is indicator of Moisture Retention

Low Resolution Proxies (More than 100,000 years)

Ocean Sediments - 25 million years Continental Sediments - 100 million years

Ice Core Gas Concentrations

Mid 18th Century: 280 ppm Early 20th Century: 300 ppm 1958: 315 ppm Now:281 ppm

Why do Monsoons occur?

Monsoon exists because land responds to solar heating more quickly than oceans.

Oxygen Isotope Thermometer. What does the O-18 concentration tell us?

More O-18 depleted ocean waters suggest more rainfall, less ice, and warmer temperature Less O-18 depleted ocean water suggests less rainfall, more ice, and colder temperature

N=

Nsubscript0 times e^(-lambda t) number of radiocarbon atoms remaining after radioactive decay at time t

Nsubscript0

Number of Radiocarbon atoms at t=0

Oxygen Isotopes

O-16 - Light Oxygen (99.8% of all oxygen) O-18 - Heavy Oxygen (.2% of all oxygen) O-18/O-16 Ratio is .0025 or 1/400 The relative amounts of these isotopes in a sample is a function of climate/environment Antarctica and Greenland have about 5% less O-18 than ocean water

Earth's Orbit Today

Orbit=elliptical; Tilt=23.5 degrees; Axis points towards north star

Position of the Continents

Originally Continents were closer together, and then slowly spread apart. Continents were at higher latitudes which allowed for more permanent ice cover. This reflected more sunlight and created a positive feedback to cause greater cooling.

Notes about climate change through the years

Over the past 550MY there have been three icehouse periods (430, 325-240, 35-0 Myr ago) Climate was warmer in past than today. Climate shifts are relatively small except when associated with continental reorganizations

Foraminifera (Two Components)

Oxygen Isotopes (in response to salinity and temperature of ocean) Replacement of Calcium with Magnesium in Skeleton - Chemical Indicator of Temperature

Principle of Uniformity

Physical and biological processes that link environmental conditions to tree growth must have been in operation in the past TREE GROWTH IS RECOGNIZABLE AND PERIODICITY DEFINABLE

Oxygen isotope ratios as a thermometer

Precipitation has a lower O-18 content than the Ocean The O-18 content of Precipitation decreases with decreasing temperature THE LESS O-18 FOUND IN THE GLACIER ICE, THE COLDER THE CLIMATE

Dating Methods: Determining the ages of our Paleoclimate Proxy Records

Primarily done via Radiocarbon Dating Techniques Establishing a Climate Record is a first order process and must be defined with highest degree of accuracy

Cross-dating

Proccess of cross-matching patterns in ring widths or other ring parameters (thickness, darkness, false rings) between trees and stands. Cross-dating must begin with ring patterns from living trees and an outside date is known.

Isotope Fractionation

Process where O-16 evaporates first and O-18 condenses first as temperature increases

BLAG hypothesis

Proposes that climate changes over the last few hundred years are mainly driven by changes in the CO2 input of the atmosphere by plate tectonic processes CHANGES IN SEAFLOOR SPREADING CONTROL DELIVERY OF CO2 Calls on the ROCK CYCLE to moderate these effects

Why use cross dating?

Provides a mean to account for ring anomalies such as missing rings and false rings. Cross dating can also provide a mean for dating DEAD WOOD

More Dating Methods

Radiometric- use of Carbon 14 and U series Incremental- Rings, Bands or Varves Correlation

Tree Remnants

Remnants are critical for extending tree-ring chronologies. Theoldest known pine tree is around 5000 years old. But using deadwood, we can get records up to 11,000 years old.

Typical O-18 Values

River - (-15%) Surface Ocean- 0 to -2% Deep Ocean - Positive 3 to 4 Ice Sheets - (-30%) in Greenland; (-55%) in Antarctica

Tectonic Scale CO2 Fluctuations

Seafloor spreading leads to increased periods of volcanic degassing of CO2 which causes warming. Higher temperature leads to INCREASED WEATHERING, which will remove CO2 from the atmosphere and reverse warming in a NEGATIVE FEEDBACK LOOP. (Slide 6 lecture 18: memorize)

What influences the tree rings?

Size Density anatomical and chemical characteristics of each growth layer can reflect environmental conditions occurring during the year of the formation.

Formation of Ice from Snow

Snowflakes gradually compress, and as this happens, become semiliquid. In a semiliquid state they are able to fill spaces more easily, and become more dense. Semiliquid crystals bond together when they touch- eventually seal as ice.. Snow is almost 90 percent air, whereas glacial ice is 20% air, and that is as bubbles.

How long have we been measuring temperature?

Started in 17th Century, but instrumental records began mid 19th century. Instrumental Records of Ocean Climate is even shorter.

Overview of reconstruction methodology

Starts with Tree Rings (PREDICTORS) and Observed Streamflow (PREDICTAND). Then one uses statistical calibration to gain a regression model, which allows you to create a reconstruction model. This Model should Validate what you observed. IF so, you can create a time series of Reconstructed Streamflow just out of Tree Rings and Observed Streamflow.

Dendroclimatology

Study of Tree Rings to provide an indirect measure of climate (and rainfall and growth of trees) High Resolution Proxy

Dendroclimatology

Study of the relationship between annual tree growth and climate. Tree rings are used to reconstruct annual, and seasonal climatic variations, up to thousands of years before human records.

Dendrochronology

Studying of Tree Rings. Can be done throughout most of the world's temperate regions, and even some tropical regions. Each tree grows one ring per year

Varved Sediments banding identification (summer and winter)

Summer- mostly biological, organic rich Winter- mostly runoff

Types of Proxy Records of Climate Change

Temperature Estimates from Ice Cores, Tree rings, Speleothems (Cave Stuff), Corals, and Marine Sediments

What determines insolation received by the Earth?

The Sun Earth distance. It will change only gradually. The spatial and temporal distribution of insolation depends on details of sun's orbit. Orbital changes are what affect the atmosphere and ocean physics, which in turn affect greenhouse gases and abledo, thus affecting climate.

Changing initial Carbon 14

The radiocarbon method assumes that C14 is constant or at least known Studies of tree rings (ring counts)have shown that C14 varies with time To address this, scientists came up with a calibration curve.

Tree Ring-Flow Relationship

The shape of the tree ring-flow relationship is generally linear, but if not, thenit is logarithmic.

Radioactive Decay

There are stable and unstable isotope nuclei Unstable Isotope Nuclei are considered RADIOACTIVE All unstable isotopes undergo RADIOACTIVE DECAY into more stable elements (Radioactive Parent Decays into Daughter atom(s))

Climate during the dinosaurs

There were NO ice caps - this meant sea level was 100-200M HIGHER. -Warmer weather leads to more intense storms and a stronger hydrologic cycle and less wind. -There will also be more plants and flowers, etc. -4-8 times more CO2 in the atmosphere (Slide 3 lecture 18-memorize)

What Are Proxy Records of Climate Change?

They are temperature estimates from ice cores, marine sediments, tree rings, speleothems, and corals

What do Lake Varves consist of?

They consist of coarse grained, light colored deposit and a finer grained, dark-colored winter deposit formed when fine sediment settles out from the water under ice cover.

Chemical Weathering

This process releases carbonic acid and ultimately adds carbon into the ocean*

Half Life

Time it takes for half of a population of a parent atom to decay into a daughter atom

Why Study Climate?

To learn about Climate Extremes, understand the effects of human activity on climate, and to determine how periodic climate change is

Principal of limiting factors

Tree growth is controlled by some limiting climatic conditions (affects all trees synchronously)

Why use tree rings as proxies?

Tree rings offer a unique paleoclimate perspective because of their ability to provide the precisely-dated, high resolution, long-term information which can be used to understand Earth's climate

Radiocarbon

Two Stable Isotopes: Carbon 12 (98.8%) and Carbon 13 (1.1%) Equilibrium exists between rate of new C-14 production in the upper atmosphere and rate of decay of C-14 in global carbon resevoir

Coral as Climate Archives

Two Types Pacific/Indian: Porites - Diploastraea Atlantic: Montastraea - Diploria - Siderastraea Coral can be used to study climate variability in the tropical surface oceans

Coral Archive Replication: Do multiple corals from the same reef record the same signal?

Yes

Core Parameters to determine the depth age relationship in an ice core

annual layering of visual stratigraphy electrical conductivity laser light scattering of dust stable isotopes major anions and cations insoluble particles Lead 210 Total Beta Activity Change in Carbon 14

concentrations from ice core records

atmospheric gas content in an ice core is a DIRECT measure of paleo-atmospheres

Radiocarbon Calculation

dN/dt= -lambdaN

t(1/2)=

ln2/lambda It is the time it takes for half the number of radiocarbon atoms in a given sample to decay is 5730 years.

Firn

porous, uncosolidated layer of snow on top of polar ice sheets. It is approximately 90 m thick at Vostok.Gas diffuses throughout and fractionate due to gravity, and temperature and concentration gradients

lambda=

radioactive decay/disintegration constant

Eccentricity

shape of the orbit: varies from being elliptical to almost circular

Obliquity

tilt of the axis of rotation Cycle of ~ 41,000 years • Varies from 22.2 to 24.5°(The current axial tilt is 23.5°) If Earth's orbit were circular, No tilt = no seasons 90° tilt = largest seasonal differences at the poles (6 mon. darkness, 6 mon. overhead sun) • Greater tilt = more intenseseasons

Precession

wobbling of the axis of rotation

Ice Cores

• Dated with volcanic ash, ice flow models • Located at high latitudes, altitudes • H2O in ice o Oxygen isotopes - temp, precipitation • Dust amounts o Global dryness, wind • Air Bubbles - Air in the Cores are a direct measurement of actual gas concentrations in bubbles trapped in the ice o Actual samples of trapped air, determine past concentrations of different gases, i.e. CO2, CH4

Change in Insolation Effects

• Precession dominates at low and middle latitudes • Tilt is more evident at higher mid-latitudes. • Eccentricity is not significant directly, but modulates the amplitude of the precession cycle. • Summer changes dominate over winter at polar latitudes.

Tree Rings

• Predominantly temperate(mid-latitudes) • Dated using radiocarbon • Thick bands during growing season, thin bands during cold/dry months • Varying widths of growth bands reflect temperature or precipitation -Stress varies growth rates

Lake Sediments

• Record terrestrial climate variations (temperature, precipitation) • Varved sediments - annual banding caused by seasonal changes in productivity, sediment input o Summer - mostly biological, organic-rich o Winter - mostly runoff • Ostracods - Oxygen isotopes of shells • Pollen/C isotopes o Changing vegetation

Corals

• Skeletons made of aragonite(CaCO3) • Dated using annual density band, U-Th, 14C • Recorders of tropical sea surface conditions: Temperature, Salinity • Oxygen Isotopes record a combination of temp and salinity • Strontium/Calcium (Sr/Ca) records mainly temperature